1. Field of the Invention
This invention relates to an apparatus and method for controlling the temperature during the regeneration of fluid catalytic conversion processes. More particularly, it relates to an improved regenerator and a method of removing heat from a bed of solid catalyst particles undergoing regeneration by combustion of carbonaceous deposits on the catalyst with an oxygen-containing gas in the regenerator of a fluid catalytic cracking unit.
2. Description of Information Disclosures
On most fluid catalytic cracking units, it is necessary to remove heat at a controllable rate from the regenerator when spent catalyst is regenerated by burning off carbonaceous material with an oxygen-containing gas, such as air, to maintain equilibrium cracking conditions since the exothermic heat of regeneration imparted to the catalyst is transmitted to the fresh oil feed to the cracking reactor. It is also necessary to remove heat continuously to prevent undue regeneration temperature levels tending to sinter or deactivate the catalyst by surface area reduction. When heavy hydrocarbonaceous feeds, such as atmospheric residua, vacuum residua and heavy crude oils are catalytically cracked, a greater amount of carbon deposits on the catalyst particles than in cracking of feeds, such as gas oil. When the spent catalyst from the catalytic cracking of such heavy hydrocarbon feeds is regenerated by combustion with an oxygen-containing gas in a regeneration vessel, the heat removal problem is further aggravated since more heat is released in the regenerator than that which can be utilized in the process.
Various methods have been proposed to remove heat from a regenerator. The heat removal has been accomplished by withdrawing a portion of the catalyst from the catalyst bed in the regenerator and circulating it through a tubular waste heat boiler so as to cool it before returning it to the catalyst bed. It is also known to use steam coils in the regenerator as a means of heat recovery and temperature control. See, for example, U.S. Pat. No. 4,009,121. When a steam coil is placed in the bed of a regenerator, the heat removed by the coil cannot readily be varied or controlled. It has now been found that the heat removal in a catalyst regenerator can be controlled by utilizing an improved regenerator.